Figure 1. A schematic introduction of XAS and in situ XAS. (a) An XAS spectrum of Pt foil at the Pt L3 edge, showing that it consists of three parts, the pre-edge (red), the XANES (cyan) and the EXAFS (green). The insets show the electron transition happening in the XANES and the interference between photoelectrons and backscattered electrons in the EXAFS. Schematic illustration of (b) in situ XAS measurements under potential control, showing that XAS is a bulk per- atom averaging technique whilst electrochemical measurements are a probe of the surface (including the near-surface, few nanometers beneath the topmost layer, depending on the reaction), and (c) approaches to achieve surface-sensitive XAS for electrocatalysts. (Huang & Russell , 2021)

The X-ray absorption near edge (XANES) region is sensitive to the oxidation state and electronic structure of the absorber. The extended X-ray absorption fine structure (EXAFS) provides information about the local coordination of the absorber, the identity and coordination number of the neighboring atoms, and the distance between the absorber and the neighbors. In comparison to other approaches for characterizing electrocatalysts, XAS has two distinct advantages. The local structure regardless of the material's degree of crystallinity.